Specimen Illumination Using Dynamic Diffuser and Diffractive Elements
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Solution Overview
Problem
Current illumination systems for semiconductor inspection using coherent light sources face challenges such as difficulty in controlling light distribution in the pupil, non-uniform light distribution in the field, high power densities leading to surface contamination and damage, and increased complexity due to multiple mechanisms required to reduce speckle and coherence.
Innovation Solution
A system that illuminates a specimen using a coherent light source with a diffuser, where the light is made to appear incoherent by modulating the diffuser's position and using diffractive optical elements to control the light pattern, ensuring uniform distribution and reduced power densities, while maintaining high brightness and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If coherent light sources are used for illumination, then brightness and resolution are improved, but speckle noise and coherence artifacts increase
Solution Approach 1:
The diffuser is dynamically modulated (rotated or vibrated) during the exposure time to change the scattering pattern continuously. This temporal variation causes the speckle pattern to shift and average out, reducing its visibility while preserving the high brightness of coherent light illumination.
Solution Approach 2:
A diffuser is introduced as an intermediary element between the coherent light source and the specimen. The diffuser scatters the coherent light to reduce spatial coherence, thereby minimizing speckle noise and coherence artifacts while maintaining sufficient brightness for high-resolution inspection.
2Object-generated harmful factors
If multiple mechanisms are added to reduce speckle and coherence, then speckle noise is reduced, but device complexity increases
Solution Approach 1:
The diffuser serves multiple functions simultaneously: it reduces spatial coherence to minimize speckle noise, controls the angular distribution of light for uniform pupil illumination, and can be dynamically modulated to further reduce coherence artifacts. This consolidation of multiple functions into a single element avoids the need for separate mechanisms.
Solution Approach 2:
The system controls the degree of coherence reduction by adjusting parameters such as the diffuser material properties, its position in the optical path, and its modulation characteristics. This allows optimization of speckle reduction while maintaining adequate brightness and resolution without adding complex mechanical systems.
3Measurement precision
If coherent light is used to illuminate the specimen, then resolution is improved, but ringing artifacts and sharp transitions increase
Solution Approach 1:
The diffuser acts as an intermediary that partially scrambles the coherent light wavefront, reducing spatial coherence enough to eliminate ringing artifacts and produce smooth transitions in the image, while preserving sufficient coherence to maintain high resolution through the objective lens.
4Object-generated harmful factors
If incoherent light sources are used, then speckle noise is reduced, but brightness and resolution decrease
Solution Approach 1:
Instead of using completely incoherent light sources with low brightness, the system uses coherent light with controlled parameters - specifically, the diffuser is optimized to reduce spatial coherence to a level that minimizes speckle while preserving temporal coherence and brightness for high-resolution imaging.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves controlled light distribution, reduced speckle noise, and lower power densities, enhancing defect detection sensitivity and system simplicity by using diffractive optical elements and modulating the diffuser's position to create an incoherent illumination effect.
Implementation Method 1
a diffuser with a predetermined pattern of coherent laser light
Implementation Method 2
using diffractive optical elements to control the light pattern
Implementation Method 3
one or more second optical elements configured to image light exiting the diffuser onto an illumination pupil of the system
Implementation Method 4
an objective lens configured to focus light from the predetermined pattern in the illumination pupil onto a specimen plane
Data Source
AI summary
Systems and methods for providing illumination of a specimen for inspection are provided. One system includes one or more first optical elements configured to illuminate a diffuser with a predetermined pattern of coherent light. The system also includes one or more second optical elements configured to image light exiting the diffuser onto an illumination pupil of the system such that the predetermined pattern is reproduced in the illumination pupil. In addition, the system includes an objective lens configured to focus light from the predetermined pattern in the illumination pupil onto a specimen plane. In one embodiment, the light focused onto the specimen plane is not substantially coherent. In another embodiment, the predetermined pattern is selected based on an illumination mode selected for the inspection of the specimen.